At present, improving the efficiency of solar cells is the goal pursued by the highly competitive photovoltaic industry. Main commercial methods to improve the efficiency of solar cells are the shallow junction method and the dense gate method. That is to say, raising the diffusion sheet resistivity and increasing the quantity of printed gate electrodes are used to improve the efficiency of solar cells.
In order to extract photo-induced current produced in a crystalline silicon solar cell to the external load, it is necessary to a make metal electrode respectively on the two sides of a silicon P-N junction and to set up a metal connection. Therefore, fabricating electrodes is a very important for solar cells.
The electrodes on the surface of silicon solar cells are mainly the back side electrode and the front side silver electrode. These electrodes are usually printed on the surface of silicon wafers by the use of conductive silver pastes.
A front side silver paste is printed by high resolution screen printing to form gate lines with a good height to width ratio, so as to reduce the shading area on the surface of the solar cell, and reduce the series resistance inside the solar cell and the internal power dissipation of the photo-induced current, and eventually, to effectively improve the photoelectric conversion efficiency of the solar cell, Thus, there is an increasingly high demand on the printability of the front side silver paste.
In addition, the front side silver paste has the ability to penetrate the SiNx antireflective film. Forming good ohmic contact with the silicon wafer after being sintering is a key factor to improve the efficiency of solar cells.
Generally, reducing the gate line width and raising gate line height to width ratio are the current topics under more research and development. The printed line array has already arrived at the bottleneck stage. In the meantime, there is very few domestic researches on the additives used for silver pastes.
Therefore, in the invention by the use of graphene which has a two-dimensional planar structure, high electrical conductivity and thermal conductivity, the ohmic contact performance between the paste and the silicon substrate is improved, the series resistance of the paste is reduced, and the photoelectric conversion efficiency of solar cells is improved.